The present invention generally relates to remote alarm transfer methods and systems, and more particularly to a remote alarm transfer method for transferring an alarm to a remote station in an asynchronous transfer mode (ATM) cross-connect unit, and a system which employs such a remote alarm transfer method.
In an ATM transmission system, it is necessary, as in the case of a conventional synchronous transfer mode transmission system, to transfer an alarm to a remote station which transmitted a signal in order to notify the remote station that the signal transmitted therefrom cannot be received.
FIG. 1 shows a conceivable ATM cross-connect unit, FIG. 2 shows an alarm transfer path, and FIG. 3 shows a path setting table.
In FIG. 2, an ATM cross-connect unit 13' is located very close to a communication station 21, and FIG. 1 shows the ATM cross-connect unit 13' assuming that no fault exists in an upstream path i and a fault is generated only in a downstream path g.
In FIG. 2, ATM cross-connect units 11', 12' and 14' respectively have only an upstream or downstream path. An ATM cross-connect unit 10' is located very close to a communication station 20, and it is assumed that no fault exists in a downstream path a and a fault is generated only in an upstream path n.
In the ATM cross-connect unit 13' shown in FIG. 1, an alarm indication signal (AIS) cell generator 3 generates an AIS cell when an abnormality detector 1 detects an abnormality in a signal path or a synchronization error detector 2 detects a non-synchronized state of its own station. The AIS cell is supplied to a cross-connect part 6'. In addition, the AIS cell generator 3 notifies that a fault is detected and the AIS cell is generated to a network management center 8' via an interface 7'.
The cross-connect part 6' outputs the AIS cell according to a path which is determined by a path setting table 5'. The path setting table 5' specifies an output path for a signal which is input via an input path.
The network management center 8' sets an alarm transfer path for sending the AIS cell to the remote (or far end) station by sending path setting information to the path setting table 5' via the interface 7' when the fault detection is notified from the ATM cross-connect unit 13'. Then, the cross-connect part 6' transfers the AIS cell to the remote station according to the path which is set in the path setting table 5'.
Next, a description will be given of a remote alarm transfer path when a fault is generated in a communication path which is set in FIG. 2.
As shown in FIG. 3(A), input and output path names are set in the path setting tables of the ATM cross-connect units 10', 11', 12', 13' and 14'. In FIG. 3, each ATM cross-connect unit is denoted by "ATMXC". For example, the communication path is set in the ATM cross-connect unit 10' so that the signal input from L of the communication station 20 via the input path a is output to the output path b, and the communication path is set in the ATM cross-connect unit 11' so that the signal input via the input path c is output to the output path d. The communication path is set similarly for the other ATM cross-connect units 12', 13' and 14' as may be seen from FIG. 3(A), and as a result, the signal input from L of the communication station 20 is output to M of the communication station 21 via the paths a, b, c, d, e, f, g and h. On the other hand, the signal from M of the communication station 21 is input to L of the communication station 20 via the paths i, j, k, l, m and n.
In this case, when a fault is generated in the path between the ATM cross-connect units 11' and 12' as shown in FIG. 2, the AIS cell is transferred downstream via the paths f, g and h. In addition, the ATM cross-connect unit 12' notifies the network management center 8' that a fault is generated and the AIS cell is transmitted.
In order to transmit the AIS cell to the remote communication station 20, the network management center 8' transmits information for setting an alarm transfer path (paths o, p, q, r and n) to the ATM cross-connect units 12', 11' and 10'.
As shown in FIG. 3(B), the ATM cross-connect units 12', 11' and 10' write the input and output path names in the respective path setting tables 5'. Therefore, the AIS cell is transferred via the paths o, p, q, r and n, and the generation of the fault is notified to the remote communication station 20.
However, according to the conceivable ATM cross-connect unit described above, the ATM cross-connect unit notifies the fault to the network management center 8' when the fault is generated, and thereafter receives the alarm transfer path setting information from the network management center 8' and sets the alarm transfer path. Then, the ATM cross-connect unit transfers the AIS cell to the remote communication station. For this reason, there are problems in that it takes a considerably long time to transfer the AIS cell to the remote communication station, and there is a delay in transferring the fault information to the remote communication station. In addition, there is also a problem in that the control of the network management center 8' becomes complex.